The microwave oven is a ubiquitous feature in modern society. However, its limitations are well known. These include, for example uneven heating and slow absorption of heat, especially for defrosting. In fact, ordinary microwave ovens, when used for defrosting and even heating, result in foods in which the outside is generally warm or even partly cooked before the interior is defrosted.
A number of papers have been published in which a theoretical analysis of the problem of warming of a cryogenic sample has been carried out. Because of the difficulties of such analysis, such analysis has only been carried out on regular shapes, such as spherical, and ellipsoidal shapes. Experimental attempts have apparently been made on kidney sized specimens, but results of these experiments do not indicate that a viable solution for defrosting kidneys is available.
Moreover, there does not appear to be a solution for defrosting other organs or foods of more arbitrary shapes.
Prior art publications include:    S. Evans, Electromagnetic Rewarming: The effect of CPA concentration and radio source frequency on uniformity and efficiency of heating, Cryobiology 40 (2000) 126-138    S. Evans, et al., Design of a UHF applicator for rewarming of cryopreserved biomaterials, IEEE Trans. Biomed. Eng. 39 (1992) 217-225    M. P. Robinson, et al., Rapid electromagnetic warming of cells and tissues, IEEE Trans. Biomed. Eng. 46 (1999) 1413-1425    M. P. Robinson, et al., Electromagnetic re-warming of cryopreserved tissues: effect of choice of cryoprotectant and sample shape on uniformity of heating, Phys. Med. Biol. 47 (2002) 2311-2325.    M. C. Wusteman, Martin et al., Vitrification of large tissues with dielectric warming: biological problems and some approaches to their solution, Cryobiology 48 (2004) 179-189.
A paper entitled “Control of Thermal Runaway and Uniformity of Heating in the Electromagnetic Warming of a Cryopreserved Kidney Phantom” by J. D. J. Penfold, et al., in Cryobiology 30, 493-508 (1993) describes a theoretical analysis and experimental results. While some experiments were apparently made with a kidney sized phantom, the main reported results are with a uniform spherical object.
As reported a cavity was fed with electromagnetic energy at 434 MHz from three orthogonal directions (x, y, z). The x and y feeds were provided from a same generator and a phase change was introduced so that the field was circularly polarized. The frequency was varied in steps of 32 kHz (apparently up to about 350 kHz maximum) to match the input impedance as it changed with increasing temperature.
An article by Ramon Risco Delgado, Jorge Aguilar Barrera: Microwaves and Vascular Perfusion: Obtaining Very Rapid Organ Cooling. Cryobiology. 2004. Page 294, describes a freezing technique, according to which an organ is cooled by perfusion of its vascular system by a non-polar coolant such as CF4 while at the same time, the organ is heated by microwaves. Microwaves heat all the tissues, but not the coolant in the vessels, due to its non-polar character. Because heating and cooling are simultaneously applied to the organ, the authors express their belief that control of the microwave power and the perfusion rate of coolant makes it possible, in principle, to keep the temperature of the organ constant at, for instance, 37° C., even though the coolant in the vascular system may be very cold, for instance, around −150° C. The authors also express their belief that “If, when this situation has been achieved, the microwaves are suddenly switched off a very high cooling rate will occur and this could, in principle, be enough to vitrify the whole organ”.
Generally, water freezing causes crystal growth and expansion that is known to damage tissue. Since crystallization is an exothermic process, a forming crystal can cause thawing of nearby crystals, followed by recrystallization during the freezing process, which may cause additional crystallization induced damage. Since much damage is caused to tissue due to crystallization and recrystallization, rapid freezing, which leaves only little time to these destructive processes to occur, is preferably applied. However, in bulky bodies (e.g. human, bovine or porcine organs, large fish or large portions thereof) rapid freezing is difficult to achieve, since the coolant cools the body from the outside and the inner portions of the body that are distant and separated from the coolant cool only by cooled adjacent portions of the body. One preferred solution that is known in the art is reducing freezing damage by directional freezing, a process where freezing is controlled such that it would take place in a specific direction
U.S. Pat. No. 5,873,254, the disclosure of which is incorporated herein by reference, describes a device for freezing biological material by moving the biological material along a temperature gradient.
WO2006/016372, the disclosure of which is incorporated herein by reference, describes directional freezing of biological material placed in tight contact with at least one, preferably between two heat exchangers, and controlling the temperature in at least one of the heat exchangers such that a freezing temperature front propagates in the biological material away from at least one of the two heat exchangers.
WO2003/056919, the disclosure of which is incorporated herein by reference, describes gradually freezing of bulky biological material in a process that may involve directional freezing.